Rubber modified polymers have been produced from vinyl aromatic monomers by a number of processes for the purpose of improving impact resistance. Typically, a rubber is mixed with a polymerized vinyl aromatic monomer, or alternatively, the vinyl aromatic monomer is polymerized in the presence of a rubber. In the latter method, the vinyl aromatic monomer is partially graft polymerized onto the rubber. Rubber modified copolymers of vinyl aromatic monomers have also been produced, such as acrylonitrile-butadiene-styrene (ABS). ABS copolymers have been produced using polymerization processes such as bulk-suspension, continuous bulk, and emulsion.